The results were published online this week in Cancer, the journal of the American Cancer Society.

"Black patients have been shown to have a poorer prognosis despite their generally younger age and earlier tumor stage at diagnosis," the paper said.

Five-year survival rates were 72.6 percent for whites, compared with 68 percent for blacks. The study concluded that whites have a "survival advantage" over black patients, except among those of both races who received surgery.

"African-Americans started out with cancers that weren't as serious, but ended up dying sooner," Wong-Ho Chow said, adding that there's no clear reason why.

According to the institute, 64,770 Americans - 40,250 women and 24,520 men - will be diagnosed with cancer of the kidney and renal pelvis in 2012. An estimated 13,570 people will die from the disease this year.

Renal cell carcinoma rates overall have been increasing for at least four decades, with African-Americans outpacing whites since at least the 1990s.

According to one UTMB physician, part of the reason the cancer may be more deadly for black patients is that whites are more likely to receive surgical treatment.

Surgery preferred

Dr. Bagi Jana, an associate professor at the UT Medical Branch at Galveston who is not involved in the study, explained that partial or radical nephrectomy - removing a kidney tumor or the entire organ - "is the treatment of choice."

According to Chow's study, 14.5 percent of black patients did not undergo surgery, compared with 10.5 percent of whites.

"It looks like African-Americans had less likelihood of undergoing nephrectomy … and that is possibly linked to increasing the chance of death," said Jana, who specializes in genito­urinary cancers.

The analysis didn't include other groups because the numbers were too small, but institute statistics show that renal cancer rates are highest among American Indians and Alaskan Natives.

The study's sample of patients came from 12 institute registries representing about 14 percent of the U.S. population including Connecticut, Hawaii, Iowa, New Mexico, Utah, 10 rural Georgia counties and the metro areas of Atlanta, Detroit, Seattle, Los Angeles, San Francisco and San Jose, Calif.

Both the paper's author and the UTMB cancer specialist said more study is needed.

Disparity a mystery

One of the suspected causes for the survival disparity is that black patients have higher rates of high blood pressure, kidney dysfunction and other conditions that may affect their candidacy for kidney cancer surgery, Jana said.

"The take-home message from the study is very clear: There is an increased chance of death in black patients with kidney cancer compared with white patients. It seems to be linked to less chance of undergoing an operation."

As to why the chance of operation is less in a black patient? "We don't know," Jana said. "Poor health is doubtful in young patients, so it could be access to care."

Chow thinks the difference could be explained by whether black patients make lifestyle changes after diagnosis, such as losing weight, reducing blood pressure and improving nutrition.

"We know that a disparity exists, so we need to be aware of it and we need to look into that further," she said.